Back-up pads are used in the abrasives field to provide support to an abrasive disc or sheet during abrading. The term "abrading" as used herein includes all methods of material removal due to frictional contact between contacting surfaces in relative motion, such as grinding, sanding, polishing, burnishing, and refining. The abrasive articles can be coated abrasives, lapping coated abrasives, or nonwoven abrasives. These abrasive articles can be in the form of a disc, sheet, or a polygon. The back-up pad includes a generally planar major surface, to which the abrasive article, such as a disc or sheet, may be attached. Although back-up pads may be hand held, back-up pads are more commonly used in conjunction with powered abrading apparatuses, such as electric or pneumatic sanders.
Abrasive discs and sheets (hereinafter "discs") may be attached to a back-up pad in one of many different ways. One popular attachment method includes an abrasive disc having pressure sensitive adhesive (PSA) on one surface thereof, such that the abrasive disc may be adhered to the major surface of the back-up pad. The major surface of the back-up pad may have, for example, a smooth foam, vinyl, or cloth surface to facilitate attachment of the abrasive disc. An example of such a back-up pad is available from the Minnesota Mining and Manufacturing Company of St. Paul, Minn. under the designation "STIK-IT" brand back-up pad. An example of an abrasive disc for attachment to that back-up pad is available from the same company under the designation "STIK-IT" brand abrasive disc.
Although they have certain benefits, PSA abrasive discs and back-up pads have some limitations. For example, the PSA can be too aggressive in its adhesion to the back-up pad, such that the operator may be unable to remove all of the abrasive article from the back-up pad. If pieces of the disc backing or areas of PSA, or both, are left on the back-up pad, the resultant buildup can cause high spots on the back-up pad and present an uneven and unbalanced operating surface for receipt of a new abrasive disc. Another potential deficiency of the PSA back-up pad is that when PSA from the abrasive article remains on the back-up pad, the PSA can become contaminated with dust and debris, resulting in a "dead" spot onto which a new disc will not adhere, or an uneven surface that can tend to leave wild scratches in the workpiece. Thus, back-up pads adapted for receipt of a pressure sensitive adhesive backed abrasive disc may be undesirable.
A second type of back-up pad includes a major surface having a plurality of hooks projecting therefrom. The hooks are adapted to engage certain structures provided on the back face of an abrasive disc to releasably attach the disc to the back-up pad. An example of such a back-up pad is available from the Minnesota Mining and Manufacturing Company of St. Paul, Minn. under the designation "HOOK-IT" brand back-up pad, and an example of an abrasive disc for attachment to that back-up pad is available from the same company under the designation "HOOK-IT" brand abrasive disc.
The hook-faced back-up pad has certain advantages, such as ease of attachment and reattachment to the abrasive disc, but it also demonstrates certain potential disadvantages. For example, repetitive engagement and disengagement of the loop-backed abrasive results in the loop fabric breaking and depositing debris between the hooks, which decreases the useful life of the back-up pad. Thus, the hook faced back-up pad may also be undesirable for some applications.
German patent DE 4 241 908, assigned to Dualflex Company, Ltd. of Ontario, Canada, discloses a back-up pad having a velvet-like material thereon. The material comprises individual fibers, some of which are connected to the back-up pad at only one end, and others which are connected to the back-up pad at both ends to form loops. This back-up pad is used with a tough, non-hardening adhesive to hold an abrasive article thereon. This backup pad can suffer from the same deficiencies as the backup pad used with a PSA disc, above, and may thus be undesirable.
It is therefore desirable to provide a back-up pad and abrasive article that overcome the disadvantages of the prior art.